Thanks for looking into it. I look forward to hearing your findings. Yes, all the folded slide guns I own fit into it perfectly. The stainless slides do not (Legacy P229 is a definite no-go but I don't actually remember whether or not I tried my milled P226 when I had it).I think that was either a P225 specific tool, or for folded slides. I'll see if I can find out for sure.
No it's stamped into the aluminum, here's another view...Thanks Willard! Mine does not have any information engraved in it whatsoever. Completely blank. The only markings I found were on the top of the little bolt head. It's marked "F-C". The bolt I am referring to is the one on the open ended side that serves the same function as the bolt with "P225/P6" next to it in your third photo.
Is your SIGARMS one (in your first photo) roll marked/engraved with that "SIGARMS" lettering or is it just painted on?
When you think about it, the early P220/P75 had the integral front sight, on the Slide, so essentially the P6/P225 was likely the first to have a dovetailed front sight. As the sight tool, I have came after the introduction of the P226, and P228 as well, the early tools would have been able to work on all carbon steel Slides.